Electrophysiology ablation procedures use energy sources, such as radio frequency (RF) energy, to ablate tissue in order to correct or prevent arrhythmias such as super ventricular tachycardia, paroxysmal atrial tachycardia or atrial fibrillation. Some procedures require the use of the catheter-delivered energy sources near the esophagus resulting in the risk of damage to the esophagus including the creation of esophageal fistula. Due to the proximity of the esophagus to the cardiac atria, it is critical for physicians to know the location of the esophagus during cardiac ablation procedures in the atria in order to minimize the risk of esophageal fistula.
Esophageal fistula associated with ablation used to treat atrial fibrillation have resulted in a high incidence of mortality. The need exists for a device or method to reduce or eliminate the risk of esophageal fistula formation by enabling the electrophysiologist to avoid damaging the esophagus with the energy source used for ablation.
Electroanatomic mapping systems enable a user to develop detailed electroanatomic maps of the heart providing three-dimensional images of the heart to users. Such systems are used to precisely guide ablation catheters to different areas of interest within a heart and can be used to decrease procedure time and reduce exposure to fluoroscopy. One such electroanatomic mapping system is the Carto system produced by Biosense Webster. Such systems that use a catheter to provide three-dimensional location information are described in U.S. Pat. No. 5,546,951 entitled “Method and Apparatus for Studying Cardiac Arrhythmias”, U.S. Pat. No. 6,368,285 entitled “Method and Apparatus for Mapping a Chamber of A Heart” and U.S. Pat. No. 6,650,927 entitled “Rendering of Diagnostic Imaging Data on a Three-Dimensional Map” which are hereby incorporated by reference.
Additionally, U.S. Pat. No. 5,738,096, which disclosure is incorporated herein by reference, describes methods for geometrical mapping of the endocardium based on bringing a probe into contact with multiple locations on a wall of the heart, and determining position coordinates of the probe at each of the locations. The position coordinates are combined to form a map of at least a portion of the heart. Once the position of the catheter is known, external sensors can be used to provide local physiological values of heart tissue adjacent to the tip of the catheter.
Further methods for creating a three-dimensional map of the heart based on these data are disclosed, for example, in U.S. Pat. No. 6,226,542, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. Position coordinates (and optionally electrical activity, as well) are initially measured at about 10 to 20 points on the interior surface of the heart. These data points are generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is preferably combined with data taken at additional points in order to generate a more comprehensive map.